Image sensing modules are commonly applied to portable mobile devices such as digital still cameras, cellular phones and PDAs (Personal Digital Assistants). Due to the mechanical limitations of those portable mobile devices, when the image sensing modules are applied to the portable mobile devices, custom-made modules are required to fit in the limitations. However, customization contradicts to the demanding requests, such as low cost, quick development and mass production.
Conventionally, an image sensing module is packaged by the following steps: forming a substrate having a cavity with a ceramic or organic material, gluing an image sensing component on the substrate, connecting the above component with electrically conductive pads inside the cavity by means of wire bonding, and covering and gluing the cavity by a window made of a transparent material like glass to obtain a structure which isolates the whole module from its surroundings and allows the light to transmit through the window, as shown in FIG. 1.
For example, Taiwanese Utility Model Patent No. 542,493, “Image Sensor Structure”, discloses an image sensor including a substrate, a flange layer, an image sensing chip and a window. The image sensing chip is provided in a recess formed between the flange layer and the substrate. One face of the flange layer is formed with signal inputs which are electrically connected with a plurality of wires, and the image sensing chip is electrically connected with the substrate by way of sides of the flange layer. The surface of the flange layer is partly coated with an adhesive layer for adhesion to the window. The flange layer is fixed to the substrate to form a recess during the process for packaging the image sensor.
Thereafter, the image sensor is soldered to a printed circuit board, and then a lens is installed to form an image sensing module. The processes for assembling such an image sensing module are classified into two fashions. First, the lens holder is glued to or fixed to the printed circuit board with screws, as shown in FIG. 2. Secondly, the lens holder is directly fixed to the image sensor, as shown in FIGS. 3 and 4.
However, some drawbacks accompany both processes. The first process is simpler to make an image sensing module, yet the area required by the module is larger. Further, surface mounting technology (referred to SMT hereinafter) and a printed circuit board (referred to PCB hereinafter) are utilized to conduct positioning between the lens and the image sensor, and therefore the error is relatively large. In the second process, the characteristics of the image sensing module vary subject to different positioning references, either on the glass or along the edge of the substrate. Furthermore, in this process, a larger transporting error occurs since the shape of the glass or the substrate is generally square and thus larger clearance between the lens and the edges of the glass/substrate is required. Additionally, since the lens holder is directly mounted on the glass, the tilting error of the whole image sensing module increases due to the error between the lens and the glass.
The present invention is proposed to eliminate the drawbacks of the prior art, and makes the following possible: smaller modules, smaller transporting and tilting errors, higher yields, better aligning precisions, lower costs, and implementation of a modulized design and a process without any precise positioning equipment.